The objective of our research is to investigate glucose and lactate metabolism in patients with malignant solid tumors, particularly colo-rectal cancer. Using isotope tracer infusion techniques, the production, utilization and oxidation of glucose and lactate will be measured under standardized conditions. The possible relationship between lactate production and tumor growth will be investigated by observations on the effect of cancer therapy on lactate metabolism. In addition, the host metabolic response to nutritional supplementation by short-term intravenous hyperalimentation will be evaluated in debilitated patients.